Window regulators of motor vehicles comprise various components designed for the raising and lowering of the pane in a window door. A window regulator is generally composed of two rails—traditionally metallic—along which slide members which secure the pane slide; the slide members are driven by actuation means manually or in motorized form, said slide members are joined to the actuation means by cables, these cables are made to pass along pulleys, which in addition to transmitting the force exerted by the actuation means, re-direct the cables which drive the slide members in order that they slide in upward or downward direction, pulling the pane. The pulleys are fixed to a base, normally a rail, through a support element with cylindrical form which acts as rotation shaft of the pulley and withstands the forces.
Each slide member is joined to the ends of two of the cables, so that when one of the cables pulls by one of its ends, the slide member moves in one direction, whilst when the other cable pulls by the other end, the slide member moves in the opposite direction.
Typically, the vehicle door is composed of a generally metal structure, different mechanisms and a door lining. Forming part of the metal structure there is a door frame, designed to house therein different mechanisms, among which we can find the window regulator, loudspeaker, lock, wiring, etc. . . . . The side of the door frame which looks towards the exterior of the vehicle is composed of a metal sheet with small orifices, basically to house the lock cylinder and the door handle. The side of the door frame which is in the inner part of the vehicle may have one or several cavities which enable the introduction and fixing of the different mechanisms, a free area remaining under the door frame, so that the pane can rise and lower without finding any obstacle in its path. To cover the cavities of the door frame inside the vehicle, the door lining is placed which, in addition to having an aesthetic and safety purpose, is the support element of some door components.
More recently is known another mounting solution called door module, composed of a pre-mounted assembly formed by a window regulator and other door components, such as, for example; a loudspeaker, a lock, wiring, etc. in this way facilitating the mounting of the assembly inside the door. The side of the door frame inside the vehicle has a sufficiently large orifice to allow the passage of the assembly which must be positioned, in a single operation, inside the door frame and later fixed to the door module.
At present, thanks to the development of thermoplastic polymers, both the window regulator bases and the door module bases can be manufactured in thermoplastic material. An advantage of using this type of materials is that it allows many design possibilities allowing a reduction both in weight and price and also enabling geometries which would be difficult to achieve with metal materials, also achieving compact and modular designs, wherein some window regulator components can be integrated, as well as other door components, reducing the number of components and their manufacturing and assembly cost.
The use of thermoplastic polymers as manufacturing materials makes it possible to achieve different degrees of integration, making the design more flexible and offering greater adaptation to a large variety of doors and configurations.
However, thermoplastic materials are less resistant than metal materials. To obtain a mechanical behaviour of a window regulator or of a module with thermoplastic components, similar to that obtained with metal materials, it is necessary to adapt the design and reinforce the assembly, for example adding ribs or giving the component walls greater thickness, penalizing part of the saving obtained by the use of thermoplastic materials. The smaller resistance of the thermoplastic materials become more critical in force concentration areas, such as, for example, in the fixing points of the pulley support elements to the bases. Furthermore, this effect is intensified with the temperature changes, becoming critical when more extreme temperatures are reached within the habitual temperatures required of the vehicles and in particular the window regulator (between −30° C. and 90° C.), wherein the thermoplastic materials suffer an important loss of mechanical properties.
For these reasons and with the possibility that both factors, force concentration points and extreme temperatures coincide in time increasing in this way the probabilities of breaking of the pulley support elements, it becomes necessary to adopt a solution which allows the distribution of forces concentrated in certain points, so that the extreme temperature changes are additionally no longer a critical factor.
In FIG. 1A an example is shown of how a pulley 20 is typically fixed to a base 10 by means of a support element 30. The support element 30 is normally composed of two parts, a cylindrical shaft 31 around which the pulley 20 rotates and an extension thereof which is a connecting element 32 fixed in a connecting area 11 of the base 10, with the cylindrical shaft 31 having a first end 33 and a second end 34.
As shown in this FIG. 1A, during operation of the window regulator, the cable 40 which drags the pane generates a force T, which is transmitted to the base 10 through the pulley 20 and the support element 30, which causes that in the material of the base 10, in the connecting area 11 with the support element 30, appear resulting forces from the reaction R which compensates the force T of the cable 40. As a consequence of the pulley thickness, the centre of action of the force T, transmitted through the pulley 20, is displaced a distance d with respect to the reaction R generated in the base 10, and therefore, generating a torque M which means the support element 30 tends to tilt, which is also supported by the material of the base 10, where additionally to the reaction R a reactive torque MR is generated so that the material of the base 10, in the connecting area 11 with the support element 30, must have sufficient rigidity to be capable of maintaining the operating position of the support element 30 and, therefore, of the pulley 20.
In FIG. 1B it is shown what occurs when during operation of the window regulator the cable 40 is subjected to a force T, and, as a consequence, a reaction R and a reactive torque MR appear in the base 10 in the connecting area 11, generating forces in the material of said area which must be withstood by the material of the base 10. As thermoplastic materials are used in its manufacturing, with less mechanical properties than the metal materials, we obtain a base 10 with less rigidity so that, against the same cable forces 40, greater deformations are produced, giving rise to a greater tilting of the support element 30, and as a consequence an increase of the distance between the centre of action of the force T to a greater value d′, which is transmitted through the pulley 20, and that of the reaction R, also therefore increasing the resulting torque MR to a greater value M′R, so that the forces withstood by the material of the base 10 in the connecting area 11 also increase.
When said forces are close to the elastic limit of the material of the base 10, this effect causes the forces to increase in the connecting area 11 of the base 10. This effect is fed back whilst the force T acts, until reaching a point wherein the elastic limit of the material of the base 10, the reactive torque MR cannot continue to increase, as the material goes from being in the area of elastic material and entering the plastic area, so that the difference between the resulting torque M′ and the resulting reactive torque M′R increases rapidly, producing the breaking of the material. The fact that the thermoplastic materials have a lower elastic limit than that of the metals increases the probability that this problem appears.
The elastic limit of the material determines the amount of forces it is capable of withstanding and decreases with temperature, i.e. it becomes lower as the temperature of said thermoplastic material increases. For that reason, forces which in normal operating conditions would not cause breaking of the material could in certain cases produce damages more easily, in the form of permanent deformations or breakings in the area of the support element 30.
In short, once the elastic limits of the material has been exceeded, if the force T of the cable 40 is maintained, permanent deformations would occur, weakening the structure and a permanent damage that tends to increase progressively, even causing breakage.
Different solutions are known wherein, with the aim of resolving the problem posed, elements are included with the objective of giving greater rigidity to the connection of the pulley support element to the base.
In patent document WO-2009/141401-A1, a solution is used comprising an intermediate metal part situated between the pulley and the base, which reinforces the connecting area between the shaft and the base, thus securing the corresponding end of the shaft, leaving the other end free, and with a flange which rests against a series of reinforcing ribs in the rail, so that when the cable pulls the pulley with a force T, the base in collaboration with the intermediate part is capable of withstanding the forces generated in the connecting area between the shaft and the base.
Patent document WO-2014/010545-A1 presents a solution which consists of a pulley support structure for a window regulator, formed by a pulley support element and a perforated shaft, capable of securely holding the pulley. The shaft is formed by a perimetral groove on the surface of one of is ends and the pulley support element consists of an orifice, the edge whereof elastically fits into the shaft groove, the perforated shaft and the pulley support element thus being mechanically linked, the pulley support structure is pre-positioned in the base of the window regulator, thanks to projections in the space which coincide with the perforations in the pulley support element, finally the window regulator is joined to the door structure by means of a threaded screw inside the perforated shaft, so that the assembly is secured to the base by one end of the perforated shaft, the support pulley being situated between the pulley and the base. The solution provided by the pulley support element is based on reinforcing the connection, by increasing its rigidity, and on resting the base of the window regulator on the door structure.
However, in any of these known solutions, although they improve the device's behaviour thanks to an increase in rigidity of the connection, there continues to be a force concentration area, as the support element is fixed only by one end, there continues appearing a torque capable of making the support element tilt and possibly break, due to exceeding the elastic limit of the material.
It is, therefore, necessary to find a way of securing the support element to the base which makes it possible to distribute the forces generated by the cable during operation of the window regulator, thus avoiding their concentration and enabling the use of structures not as rigid as metal and without renouncing the advantages provided by the use of thermoplastic materials, avoiding that those forces exceed the maximums withstood by said materials.